Many current multi-color image forming devices build up an image on an intermediate and then transfer the color image in one step to paper. The best setting of transfer parameters, such as bias transfer roll voltage and current for the second transfer onto the paper, depends upon many factors, including the specific paper type aid current environmental conditions such as humidity and temperature.
To accommodate this, conventional image forming devices have provided limited adjustments or pre-set configurations that vary the parameters to adapt to certain contemplated conditions. Typically, this is achieved by predefining a limited set of reasonable settings in a look-up table. These are usually based on paper weight and include 3-5 broad categories to accommodate standard paper stock. The table may also be based on environmental conditions, such as high, low or moderate humidity conditions.
Although these procedures are an approximation of existing conditions, there is no guarantee that these will be the optimal settings for a given printing condition or paper stock. Instead, these predefined limited settings can lead to transfer losses of 10% or more.
Other methods and systems are known to control image transfer settings, such as through closed loop control. An example of this is U.S. Pat. No. 7,054,568 to Mizes et al., commonly assigned to Xerox Corporation, which provides a closed-loop control system that uses a full width array (FWA) area coverage sensor to measure residual mass per unit area (RMA) after transfer. Output from the sensor is used as feedback to control subsequent image transfer settings.
Other systems monitor patch density, but are media independent by taking measurements without actual transfer to a specific media type. Thus, they assist in control and formation of toner images on an intermediate transfer member, but do not account for second transfer efficiency, which will vary by transfer media type.